Positive active material composition for rechargeable lithium battery and method of preparing positive electrode using same

ABSTRACT

A positive active material composition for a rechargeable battery includes a positive active material selected from compounds represented by formulas 1 to 13, and at least one semi-metal, metal or oxides thereof:
 
Li x MnA 2   ( 1 )
 
Li x MnO 2−z A z   ( 2 )
 
Li x Mn 1−y M′ y A 2   ( 3 )
 
Li x Mn 2 A 4   ( 4 )
 
Li x Mn 2 O 4−z A z   ( 5 )
 
Li x Mn 2−y M′ y A 4   ( 6 )
 
Li x BA 2   ( 7 )
 
Li x BO 2−z A z   ( 8 )
 
Li x B 1−y M″ y A 2   ( 9 )
 
Li x B 1−y M″ y O 2−z A z   ( 10 )
 
Li x NiCoO 2−z A z   ( 11 )
 
Li x NiCoO 2−z A z   ( 12 )
 
Li x Ni 1−y−z Co y M″ z A 2   ( 13 )
where 1.0≦x≦1.1, 0.01≦y≦0.1, 0.01≦z≦0.5, M′ is at least one transition metal or lanthanide metal selected from Al, Cr, Co, Mg, La, Ce, Sr, or V, M″ is at least one transition metal or lanthanide metal selected from Al, Cr, Mn, Fe, Mg, La, Ce, Sr or V, A is selected from 0, F, S or P, and B is Ni or Co.

The present patent application is a Divisional of application Ser. No.09/579,576 filed May 25, 2000, entitled POSITIVE ACTIVE MATERIALCOMPOSITION FOR RECHARGEABLE LITHIUM BATTERY AND METHOD OF PREPARINGPOSITIVE ELECTRODE USING SAME, which claims priority from Korean PatentApplication No. 99-18802, filed on May 25, 2000, Korean PatentApplication No. 99-18803 filed on May 25, 2000, Korean PatentApplication 99-34414 filed on Aug. 19, 1999 and Korean PatentApplication No. 99-42394 filed on Oct. 1, 1999.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on applications Nos. 99-18802, 99-18803,99-34414, and 99-42394 respectively filed in the Korean IndustrialProperty Office on May 25, 1999, May 25, 1999, Aug. 19, 1999, and Oct.1, 1999, the content of which are incorporated hereinto by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a positive active material compositionfor a rechargeable lithium battery and a method of preparing a positiveelectrode using the same and, more particularly, to a positive activematerial composition for a rechargeable lithium battery exhibiting longcycle life characteristics.

2. Description of the Related Art

Rechargeable lithium batteries employ materials into or from whichlithium ions are intercalated or deintercalated as negative and positiveactive materials.

Metallic lithium has been used as the negative active material inrechargeable lithium batteries. However, lithium metal has goodreactivity toward electrolyte and deposits to form a dendric layer whichinduces short circuits between the negative and positive activematerial. There are at least two disadvantageous effects that arise fromthe reaction of lithium with electrolyte. One is the exothermicliberation of heat and the other is the formation of passive films onlithium, which has been shown to be one of the reasons for the loss ofcapacity of lithium cells upon repeated cycling.

The problem of lithium reactivity toward the electrolyte is addressed byreplacing lithium metal with carbon-based materials. With the use ofcarbon-based active materials, the potential safety problem present inmetallic lithium-based batteries can be prevented while achieving arelatively higher energy density as well as a reasonable shelf life.

For the positive active material in the rechargeable lithium battery,chalcogenide compounds into or from which lithium ions are inserted orextracted are used. Typical examples of the positive active materialinclude LiCoO₂, LiMn₂O₄, LiNiO₂, LiNi_(1−x)Co_(x)O₂(0<X<1) or LiMnO₂.LiCoO₂ is widely used as it has an electrical conductivity of about 10⁻²to 1 S/cm at room temperature and high battery voltage, but has poorsafety characteristics during high rate charges and discharges. LiNiO₂has a high charge capacity, but is difficult to produce. Manganese-basedmaterial such as LiMn₂O₄ or LiMnO₂, etc. is easiest to prepare, is lessexpensive than the other materials, and has environmentally friendlycharacteristics. Such manganese-based compounds have low capacities, butLiMn₂O₄ is particularly stable for the battery use and thus attractivefor electric vehicle application.

However, when a battery using manganese-based materials such as LiMn₂O₄is charged and discharged for a long time, particularly, at a hightemperature, a side reaction between the electrolyte and themanganese-based material occurs at the surface of the manganese-basedmaterial. It is believed that H₂ 0 reacts with LiPF₆ in the electrolyteto generate strong acid such as hydrogen fluoride (HF) which attacks theMn present on the surface of the manganese-based active material and theattacked Mn is eluted into the electrolyte. The eluted Mn is dissolvedin the electrolyte and the active material disintegrates. This sidereaction seriously deteriorates the cycle life characteristics of thebattery.

An attempt to solve this problem has been made by synthesizing amaterial including 1 or more equivalent Li or by partially substitutingoxygen with F in a spinel manganese-based material. However, thesemethods do not effectively improve the cycle life characteristics of thebattery, particularly, at high temperatures.

Furthermore, such problem due to the reaction between the positiveactive material and the electrolyte may occur in manganese-based activematerial as well as in cobalt- and nickel-based active materials.Therefore, the studies to reduce the reaction between the positiveactive material and the electrolyte are attempted, but the satisfiedeffect is not obtained.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a positive activematerial composition for a rechargeable lithium battery exhibiting longcycle life characteristics.

It is another object to provide the positive active material compositionfor a rechargeable lithium battery exhibiting good high-temperaturecycle life characteristics.

It is still another object to provide the positive active materialcomposition for a rechargeable lithium battery exhibiting thermalstability.

It is yet still another object to provide a method of preparing apositive electrode using the same.

These and other objects may be achieved by the positive active materialcomposition including a positive active material and an additive. Thepositive active material includes a lithiated transition metal compoundand the additive is selected from semi-metals, metals or oxides thereof.

The positive active material is selected from lithiated transition metalcompounds represented by formulas 1 to 13 below and the semi-metal isselected from Si, B, Ti, Ga, Ge, or Al and the metal is selected fromCa, Mg, Sr or Ba.Li_(x)MnA₂  (1)Li_(x)MnO_(2−z)A_(z)  (2)Li_(x)Mn_(1−y)M′_(y)A₂  (3)Li_(x)Mn₂A₄  (4)Li_(x)Mn₂O_(4−z)A_(z)  (5)Li_(x)Mn_(2−y)M′_(y)A₄  (6)Li_(x)BA₂  (7)Li_(x)BO_(2−z)A_(z)  (8)Li_(x)B_(1−y)M″_(y)A₂  (9)Li_(x)B_(1−y)M″_(y)O_(2−z)A_(z)  (10)Li_(x)NiCoA₂  (11)Li_(x)NiCoO_(2−z)A_(z)  (12)Li_(x)Ni_(1−y−z)Co_(y)M″_(z)A₂  (13)(where 1.0≦x≦1.1, 0.01≦y≦0.1, 0.01≦z≦0.5, M′ is at least one transitionmetal or lanthanide metal selected from Al, Cr, Co, Mg, La, Ce, Sr, orV, M″ is at least one transition metal or lanthanide metal selected fromAl, Cr, Mn, Fe, Mg, La, Ce, Sr, or V, A is selected from O, F, S or P,and B is Ni or Co).

In order to achieve these objects and others, the present inventionprovides a method of preparing a positive electrode for a rechargeablelithium battery. In this method, a positive active material is mixedwith an additive. The positive active material is selected fromlithiated transition metal compounds, and the additive is semi-metals,metals or oxides thereof. The lithiated transition metal compounds arerepresented by formulas 1 to 13. The semi-metal is selected from Si, B,Ti, Ga, Ge, or Al, and the metal is selected from Ca, Mg, Sr or Ba. Anorganic solvent is added to the mixture to prepare a positive activematerial composition and the positive active material composition isapplied on a current collector. Next, the current collector coated withthe positive active material composition is dried.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention, and many of the attendantadvantages thereof, will be readily apparent as the same becomes betterunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying, wherein:

FIG. 1 is a graph illustrating high-temperature cycle lifecharacteristics of rechargeable lithium batteries of Example 1 andComparative Example 1;

FIG. 2 is a scanning electron microscope (SEM) photograph of a positiveelectrode for a rechargeable lithium battery according to Example 4 ofthe present invention;

FIG. 3 is a SEM photograph of a positive electrode for a rechargeablelithium battery according to Comparative Example 3;

FIG. 4 is a graph illustrating energy dispersive X-ray analysis (EDX)results of a positive electrode according to Example 4 of the presentinvention;

FIG. 5 is a graph illustrating EDX result of a positive electrodeaccording to Comparative Example 3;

FIG. 6 is a graph illustrating differential scanning calorimetry (DSC)results of positive electrodes according to Example 4 and ComparativeExample 3 of the present invention;

FIG. 7 is a graph illustrating high-temperature cycle lifecharacteristics of rechargeable lithium batteries according to Example 4and Comparative Example 3 of the present invention;

FIG. 8 is a graph illustrating X-ray diffraction (XRD) pattern ofpositive electrodes according to Examples 5 to 6 and Comparative Example3 of the present invention;

FIG. 9 is a graph illustrating room temperature cycle lifecharacteristics of rechargeable lithium batteries according to Example 7and Comparative Example 4 of the present invention;

FIG. 10 is a graph illustrating cycle life characteristics ofrechargeable lithium batteries according to Example 8 and ComparativeExample 5 of the present invention;

FIG. 11 is a graph illustrating DSC results of positive electrodesaccording to Example 8 and Comparative Example 5 of the presentinvention;

FIG. 12 is a graph illustrating room-temperature cycle lifecharacteristics of rechargeable manganese-based lithium half-cellsaccording to Example 12 and Comparative Example 7 of the presentinvention;

FIG. 13 is a graph showing high-temperature cycle life characteristicsof rechargeable cobalt-based lithium full cells according to Example 13and Comparative Example 8 of the present invention;

FIG. 14 is a graph showing high-temperature cycle life characteristicsof rechargeable manganese-based lithium full cells according to Example19 and Comparative Example 11 of the present invention;

FIG. 15 is a graph illustrating DSC results of positive electrodesaccording to Example 23 and Comparative Example 13 of the presentinvention;

FIG. 16 is a graph showing cycle life characteristics of rechargeablelithium half-cell at room temperature and high temperature according toExample 23; and

FIG. 17 is a graph showing high-temperature cycle life characteristicsof rechargeable lithium coin-type half cell according to Examples 22 and23, and Comparative Example 13.

DETAILED DESCRIPTION OF THE INVENTION

A positive active material used in the present invention includesmanganese-, cobalt- or nickel-based active material. Among thesematerials, the manganese active material such as LiMn₂O₄ hasenvironmentally friendly characteristics and is less expensive than theother materials. Such manganese-based compounds are particularly stablefor battery use and thus attractive for electric vehicle application.Further, cobalt-based active material such as LiCoO₂ has a goodelectrical conductivity and high battery voltage. Finally, nickel-basedactive material such as LiNiO₂ has a high charge capacity and is aneconomical material.

Useful manganese-based positive active materials are 3V grade-positiveactive material represented by the formulas 1 to 3 and 4V grade-positiveactive material represented by the formulas 4 to 6. Cobalt- ornickel-based positive active material includes cobalt- or nickel-basedactive material represented by the formulas 7 to 10, orcobalt-nickel-based active material represented by the formulas 11 to13.

The positive active material composition of the present inventionincludes additives. The additives are semi-metals, metals or oxidesthereof. The semi-metals, metals or oxides thereof improve dischargecapacity and high C-rate cycle life characteristics, particularly, highC-rate and high temperature cycle life characteristics. Usefulsemi-metals or oxides thereof may be at least one Si, B, Ti, Ga Ge orAl, or oxides thereof. The exemplary of such semi-metal oxide is SiO₂.Useful metals or oxides thereof may be at least one Ca, Mg, Sr or Ba, oroxides thereof and the exemplary thereof may be CaO, MgO, SrO or BaO.The amount of the additives is 0.01 to 10 wt % of the positive activematerial. If the amount of the additives is less than 0.01 wt %, theeffect of addition of the additives is not induced. Whereas, if theamount thereof is more than 10 wt %, the excess additives may act asimpurities and adverse effects may be obtained.

The semi-metal, metals or oxides thereof of the present invention hasgood reactivity with HF. Although an electrolyte in a rechargeablelithium battery generally uses non-aqueous electrolyte, a trace of watermay still be included in the electrolyte. The water reacts with lithiumsalts such as LiPF₆ in the electrolyte to produce a strong acid such asHF. HF attacks Mn present in a surface of manganese-based activematerial and this Mn is dissolved in the electrolyte. As a result, theactive material is disintergrated. Due to this problem, the cycle lifecharacteristics, particularly at high temperatures, is remarkablyreduced. Whereas, since the positive active material of the presentinvention includes semi-metal or metal having good reactivity with HF,the semi-metal or metal reacts with HF such that HF is unable to attackMn. Accordingly, Mn is not eluted into the electrolyte and the activematerial is not disintergrated. If SiO₂ is used for as the semi-metals,SiO₂ reacts with HF to generate fluoride compounds such as H₂SiF₆. IfCaO, MgO, SrO or BaO is used for the semi-metal, it reacts with HF togenerate CaF₂, MgF₂, SrF₂ or BaF₂, respectively. Because the generatedfluoride compounds are solid, they do not cause the increases in theinternal pressure of the battery. Furthermore, CaF₂ exhibiting goodconductivity may use for the active material and CaF₂ can improve theperformance of the battery.

As described above, such problem due to the reaction between the activematerial and the electrolyte may occur in manganese-based activematerial as well as in cobalt- and nickel-based active materials. Thepresent invention is applied to not only the manganese-based activematerial but also to cobalt- and nickel-based active materials.Accordingly, the present invention can provide cobalt- or nickel-basedactive material with improved thermal stability and exhibits improveddischarge capacity and good cycle life at a high C-rate, particularly athigh temperatures.

The positive active material composition of the present invention mayfurther include an organic solvent. The exemplary of the organic solventis N-methylpyrrolidone.

The positive active material composition of the present invention mayfurther include a binder in order to improve adhesion between thepositive active material and a current collector. The binder may be anyone of the binders known in the related arts. The exemplary of thebinder may be polyvinylidene fluoride. The current collector may bealuminum foil, but is not limited to this. Furthermore, the positiveactive material composition of the present invention further includes aconductive agent. The conductive agent may be any one of the conductiveagents known in the related arts. The exemplary of the conductive agentmay be carbon black.

A positive electrode preparation using the composition of the presentinvention will now be described in more detail.

Lithium salt is mixed with a metal compound in a desirable ratio. Thelithium salt may be lithium nitrate, lithium acetate, or lithiumhydroxide. The metal compound may be a manganese compound for amanganese-based active material, or a cobalt and/or a nickel compoundfor a cobalt-nickel-based active material. The manganese compound may bemanganese acetate or manganese dioxide. The cobalt compound may becobalt hydroxide, cobalt nitrate or cobalt carbonate. The nickelcompound may be nickel hydroxide, nickel nitrate or nickel acetate. Themanganese, cobalt, or nickel compounds are not limited to the abovecompounds. In addition, a fluorine salt such as LiF, a sulfide salt suchas NaS, or a phosphorous salt such as H₃PO₄ may be further used.

At this time, in order to facilitate the reaction of lithium salts andthe metal compound, a solvent is added to the mixture. The solvent maybe ethanol, methanol, water or acetone. Then, the mixture is mortargrinder mixed until a solvent-free condition is reached.

The resulting mixture is heat-treated at 400 to 600° C. to produce asemi-crystalline positive active material precursor powder. Thereafter,the heat-treated active material precursor powder is dried and theprecursor powder is remixed to uniformly mix under conditions ofcirculating dry air. Alternatively, the remixing step may also beperformed after the heat-treating step.

The semi-crystalline precursor powder is again heat-treated at 700 to900° C. for about 12 hours to produce a crystalline positive activematerial. The heat-treating step is preferably performed underconditions of circulating dry air or oxygen because a uniformcrystalline active material can then be produced.

To the resulting positive active material, a semi-metal, metal or oxidethereof is added. At this time, the amount of the semi-metal, metal oroxide thereof is 0.01 to 10 wt % of the positive active material. Thepositive active material may be either the resulting positive activematerial or a positive active material which are available by commercialpurchased.

The mixture is mixed with a conductive agent, a binder, and a solventsuch as N-methylpyrrolidone to produce a positive active material slurrycomposition. A positive electrode is produced by a tape-casting methodwhere the positive active material slurry composition is coated on acurrent collector such as Al foil and the coated current collector isthen dried.

With the positive electrode, and a negative electrode and non-aqueouselectrolyte, a rechargeable lithium battery is manufactured. Negativeelectrode preparation is well known in the related art, and theexemplary thereof is that a negative active material slurry including anegative active material and a binder such as polyvinylidene fluoride iscoated on a current collector such as Cu foil and the coated currentcollector is dried. The negative active material may be carbonaceousmaterial generally used a rechargeable lithium battery.

The electrolyte may be a liquid type electrolyte or a gel typeelectrolyte. The liquid type electrolyte includes an organic solvent andlithium salt dissolved in the organic solvent. The organic solvent maybe cyclic carbonate such as ethylene carbonate or methylene carbonate,or linear carbonate such as dimethyl carbonate, diethyl carbonate,ethylmethyl carbonate or methylpropyl carbonate. The lithium salt may bea salt having the ability of facilitating the movement of lithium ionsbetween the positive and the negative electrodes. The exemplary thereofare LiPF₆, LiAsF₆, LiCF₃SO₃, LiN(CF₃SO₂)₃, LiBF₆ or LiClO₄.

The gel type polymer electrolyte is prepared by immersing the liquidtype electrolyte into a polymer film and evaporating the solvent fromthe film. If the gel type polymer electrolyte is used, it is not need touse an additional separator. The separator uses a porous polymer filmsuch as polypropylene, or polyethylene.

Accordingly, a rechargeable lithium battery with the positive activematerial of the present invention exhibits improved discharge capacityand good cycle life at a high C-rate, particularly at high temperatures.

The following examples further illustrate the present invention.

EXAMPLE 1

LiOH and MnO₂ were weighed in the mole ratio of 1/2 of Li/Mn and LiOHand MnO₂ were put into a mortar. Ethanol of a sufficient amount tocompletely react the mixture was added to the mixture and a mortargrinder-mixing step was performed till an ethanol-free condition wasobtained.

The resulting mixture was initially heat-treated at 450□ for 5 hoursunder a dry air atmosphere to produce a semi-crystalline precursorLiMn₂O₄ powder. The semi-crystalline powder was re-mixed at roomtemperature to uniformly distribute lithium salts in the mixture. There-mixed semi-crystalline was again heat-treated at 750□ for 12 hoursunder a dry air atmosphere to produce crystalline LiMn₂O₄ powder. Thecrystalline LiMn₂O₄ powder was identified by SEM and analyzed by XRD.

The crystalline LiMn₂O₄ was mixed with Si powder (particle diameters ofless than 325 nm, Aldrich, Co.). At this time, the amount of Si powderwas 5 wt % of LiMn₂O₄. The mixture was mixed with Super P carbon as aconductive agent, KF-1300 polyvinylidene fluoride as a binder andN-methylpyrrolidone as a solvent to produce a positive active materialslurry composition. At this time, the ratio of the LiMn₂O₄ activematerial and Si powder mixture: the conductive agent: binder was 94:3:3wt %. The slurry was cast into a tape shape to form a positiveelectrode. The positive electrode was then assembled with a lithiummetal foil (counter electrode), and a lithium salt solution was added asan electrolyte to thereby fabricate a coin-cell type half-cell. Thelithium salt solution included ethylene carbonate and dimethyl carbonateas a solvent and 1M LiPF₆ as a solute.

Comparative Example 1

LiOH and MnO₂ were weighed in the mole ratio of 1/2 of Li/Mn and LiOHand MnO₂ were put into a mortar.

The resulting mixture was initially heat-treated at 450□ for 5 hoursunder a dry air atmosphere to produce a semi-crystalline precursorLiMn₂O₄ powder. The semi-crystalline powder was re-mixed at roomtemperature to uniformly distribute lithium salts in the mixture. There-mixed semi-crystalline powder was again heat-treated at 750□ for 12hours under dry air to produce crystalline LiMn₂O₄ powder. Thecrystalline LiMn₂O₄ powder was identified by SEM and analyzed by XRD.

92 wt % of the crystalline LiMn₂O₄ was mixed with 4 wt % of Super Pcarbon as a conductive agent and 4 wt % of KF-1300 polyvinylidenefluoride as a binder in N-methylpyrrolidone as a solvent to produce apositive active material slurry composition. The slurry was cast into atape shape to produce a positive electrode. The positive electrode wasthen assembled with a lithium metal foil (counter electrode), and alithium salt solution is added as an electrolyte to thereby fabricate acoin-cell type half-cell. The lithium salt included ethylene carbonateand dimethyl carbonate as a solvent and 1M LiPF₆ as a solute.

The cycle life characteristics at high temperature (50° C.) of cellsaccording to Example 1 and Comparative Example 1 were measured. At thistime, the charge and discharge cycles were repeated one time to 0.1 C,three times to 0.2 C, 10 times to 0.5 C and 66 times to 1 C, at 4.3 to3.0V. The results are presented in FIG. 1. As shown in FIG. 1, thecapacity of the cell according to Example 1(a) is reduced by about 15.4%after 66 cycles at a high-rate (1 C charge and discharge). In otherwords, the capacity maintenance was 84.4%. Whereas, the capacity of thecell according to Comparative Example 1(b) is reduced by about 73.4% ata high-rate (1 C charge and discharge). In other words, the capacitymaintenance was about 26.6%. Accordingly, the active material of thepresent invention has more stability at high temperature and a high rate(1 C charge and discharge) than does the conventional active material,and also has a limited amount capacity reduction as well as good cyclelife characteristics.

EXAMPLE 2

A rechargeable lithium cell was manufactured by the same procedure as inExample 1 except that 10 wt % of Si powder (particle diameters of lessthan a 325 mesh, Aldrich, Co.) of crystalline LiMn₂O₄ was added toproduce crystalline LiMn₂O₄ powder.

EXAMPLE 3

A rechargeable lithium cell was manufactured by the same procedure as inExample 1 except that 5 wt % of B powder (particle diameters of lessthan a 325 mesh, Aldrich, Co.) of crystalline LiMn₂O₄ was added toproduce crystalline LiMn₂O₄ powder.

Comparative Example 2

A rechargeable lithium cell was manufactured by the same procedure as inComparative Example 1 except that ethanol of sufficient amount tocompletely react the mixture was added to the mixture and a mortargrinder-mixing step was performed till an ethanol-free condition wasobtained.

The high-temperature cycle life characteristics of cells according toExamples 2 to 3 and Comparative Example 2 exhibited similar with that ofExample 1 and thus, the cells according to Examples 2 and 3 have morestability at high temperature and a high rate (1 C charge and discharge)than do the cells of Comparative Example 2 and also have a limitedamount capacity reduction as well as good cycle life characteristics.

EXAMPLE 4

LiMn₂O₄ (manufactured by Nikki Co. under LM4) positive active materialpowder was mixed with Si powder. At this time, the amount of Si was 1 wt% of the positive active material. This mixture, polyvinylidene fluorideas a binder, and Super P carbon as a conductive agent were added toN-methyl pyrrolidone as a solvent to produce a positive active materialslurry composition. The ratio of the positive active material powder andSi powder mixture: the binder: the conductive agent was 94:3:3 wt %.

The positive active material slurry composition was coated on Al-foil.The coated foil was dried in an oven at 120° C. for 3 hours and thedried foil was pressed to produce a positive electrode. The positiveelectrode was then assembled with a lithium metal foil (counterelectrode), and a lithium salt solution was added as an electrolyte tothereby fabricate a coin-cell type half cell. The lithium salt solutionincluded ethylene carbonate and dimethyl carbonate (1:1 volume ratio) asa solvent and IM LiPF₆ as a solute.

Comparative Example 3

LiMn₂O₄ (manufactured by Nikki Co. under LM4) positive active materialpowder, polyvinylidene fluoride as a binder, and Super P carbon as aconductive agent were added to N-methylpyrrolidone as a solvent toprepare a positive active material slurry composition. At this time, theratio of the positive active material powder: the binder: the conductiveagent was 94:3:3 wt %.

The positive active material slurry composition was coated on Al-foil.The coated Al-foil was dried in an oven at 120° C. for 3 hours and thecoated foil was pressed to produce a positive electrode. The positiveelectrode was then assembled with a lithium metal foil (counterelectrode) to thereby fabricate a coin-cell type half-cell.

SEM photographs of the positive electrodes according to Example 4 andComparative Example 3 are presented in FIGS. 2 and 3, respectively. Asshown in FIG. 2, Si powder was on the surface of the positive electrodeaccording to Example 4. The EDX analysis method is a quantitativeanalysis and the EDX result is information about the metal component inthe positive electrode. In order to identify Si on the positiveelectrode, the EDX results of the positive electrodes according toExample 4 and Comparative Example 3 are presented in FIGS. 4 and 5. A Sipeak occurs in FIG. 4 of Example 4, but no Si peak occurs in FIG. 5 ofComparative Example 5. It is shown that the positive electrode accordingto Example 4 included Si and that according to Comparative Example 3 didnot included Si.

After the cells according to Example 4 and Comparative Example 3 werecharged at 4.3V, differential scanning calorimetry (DSC) was measured inorder to identify the thermal stability of the positive active material.The results are presented in FIG. 6. The positive active material in theelectrode of Example 4 was 0.0175 g and that of Comparative Example 3was 0.0239 g. The charge capacity of Example 4 was 114 mAh/g and thecharge capacity of Comparative Example 3 was 103 mAh/g. Though the cellof Example 4 used less positive active material than that of ComparativeExample 3, it exhibited a higher charge capacity than that ofComparative Example 3. Furthermore, as shown in FIG. 6, the positiveelectrode according to Example 4 with Si had no exothermic peaks,whereas that according to Comparative Example 3 without Si had anexothermic peak. When the cell is charged, the manganese active materialis converted into unstable L_(1−x)Mn₂O₄ of which a bond between metaland oxygen (Mn—O) is easily broken to generate oxygen. The generatedoxygen reacts with metal at high temperature to emit heat and theemitted heat causes the exothermic peak occurrence. It is shown that asthe exothermic peak area is small, and that the reactivity of thepositive active material with the electrolyte is reduced. Accordingly,since the active material according to Example 4 has no exothermic peak,it has excellent stability.

The high-temperature (50° C.) cycle life characteristics of cellsaccording to Example 4 and Comparative Example 3 were measured. At thistime, the charge and discharge cycles were repeated one time to 0.1 C,three times to 0.2 C, 10 times to 0.5 C, and 86 times to 1 C, at 4.3 to3.0V. The results are presented in FIG. 7. As shown in FIG. 7, thecapacity of the cell according to Example 4 is slightly reduced at ahigh-rate (1 C charge and discharge) and high temperature (50° C.).Whereas, the capacity of the cell according to Comparative Example 3(b)exhibited extremely reduced capacity loss at a high-rate (1 C charge anddischarge). Accordingly, the active material of the present inventionhas more stability at high temperatures and a high rate (1 C charge anddischarge) than the conventional active material and has a limitedamount capacity reduction as well as good cycle life characteristics.

EXAMPLE 5

A rechargeable lithium cell was manufactured by the same procedure as inExample 4 except that 5 wt % of Si powder of the positive activematerial was added to the positive active material.

EXAMPLE 6

A rechargeable lithium cell was manufactured by the same procedure as inExample 4 except that 10 wt % of Si powder of the positive activematerial was added to the positive active material.

The XRD patterns of the positive electrode according to Examples 5-6 andComparative Example 3 are shown in FIG. 8. In FIG. 8, the XRD patternaccording to Examples 5-6(b, c) occur a Si peak, but that according toComparative Example 3(a) occur no Si peak. These results indicate thatthe surface of the positive electrode according to Examples 5-6 includesSi.

EXAMPLE 7

A rechargeable lithium cell was manufactured by the same procedure as inExample 4 except that 1.3M LiPF₆ in a mixed organic solvent of ethylenecarbonate, dimethyl carbonate and propylene carbonate (45:40:15 volumeratio) was used for an electrolyte.

Comparative Example 4

A rechargeable lithium cell was manufactured by.the same procedure as inComparative Example 3 except that 1.3M LiPF₆ in a mixed organic solventof ethylene carbonate, dimethyl carbonate, and propylene carbonate(45:40:15 volume ratio) was used for an electrolyte.

The cycle life characteristics at room temperature of the positiveactive materials according to Example 7 and Comparative Example 4 weremeasured. At this time, the charge and discharge cycles were repeatedone time to 0.1 C, three times to 0.2 C, 10 times to 0.5 C, and 86 timesto 1 C, at 4.3 to 3.0V. The results are presented in FIG. 9. As shown inFIG. 9, the capacity of the cell of Example 7 is slightly reduced athigh-rate (1 C charge and 1 C discharge) and room temperature (20□).Whereas, the capacity of the cell according to Comparative Example 4 isextremely reduced. Accordingly, the positive active material of thepresent invention has more stability at high temperature and a high rate(1 C charge and discharge) than does the conventional active materialand has a limited amount capacity reduction as well as good cycle lifecharacteristics.

EXAMPLE 8

LiNi_(0.9)Co_(0.1)Sr_(0.002)O₂ (manufactured by Honjo Co.) positiveactive material powder was mixed with Si powder. At this time, theamount of Si powder was 1 wt % of the positive active material powder.The mixture, polyvinylidene fluoride as a binder and Super P carbon as aconductive agent were added to N-methyl pyrrolidone as a solvent toprepare a positive active material slurry composition. The mixing ratioof the positive active material and Si powder mixture: the binder: theconductive agent was 94:3:3. The positive active material slurrycomposition was coated on Al-foil. The coated Al-foil was dried at 120□for 3 hours and the dried foil was pressed to make a positive electrode.The positive electrode was then assembled with a lithium metal foil(counter electrode), and a lithium salt solution is added as anelectrolyte to thereby fabricate a coin-cell type half-cell. The lithiumsalt solution included ethylene carbonate and dimethyl carbonate (1:1volume ratio) as a solvent and 1M LiPF₆ as a solute.

EXAMPLE 9

A rechargeable lithium cell was manufactured by the same procedure as inExample 8 except that 5 wt % of Si was added to the positive activematerial.

Comparative Example 5

LiNi_(0.9)Co_(0.1)Sr_(0.002)O₂ (manufactured by Honjo Co.) positiveactive material powder, polyvinylidene as a binder and Super P carbon asa conductive agent were added to N-methyl pyrrolidone as a solvent tomake a slurry. At this time, the ratio of the positive active materialpowder: the binder: the conductive agent was 94:3:3 wt %.

The positive active material slurry composition was coated on Al-foil.The coated Al-foil was dried in an oven at 120° C. for 3 hours and thedried foil was pressed to produce a positive electrode. The positiveelectrode was then assembled with a lithium metal foil (counterelectrode).

EXAMPLE 10

LiCoO₂ (manufactured by Nippon Chemical Co. under C-10) was mixed withSi powder. At this time, the amount of Si powder was 1 wt % of thepositive active material. The mixture, polyvinylidene as a binder andSuper P carbon as a conductive agent were added to N-methyl pyrrolidoneas a binder to make a positive active material slurry composition. Theratio of the positive active material powder and Si powder mixture: thebinder: the conductive agent was 94:3:3.

The positive active material slurry composition was coated on Al-foil.The coated foil was dried in an oven at 120° C. for 3 hours and thedried foil was pressed to produce a positive electrode. The positiveelectrode was then assembled with a lithium metal foil (counterelectrode), and a lithium salt solution was added as an electrolyte tothereby fabricate a coin-cell type half-cell. The lithium salt solutionincluded ethylene carbonate and dimethyl carbonate (1:1 volume ratio) asa solvent and 1M LiPF₆ as a solute.

EXAMPLE 11

A rechargeable lithium cell was manufactured by the same procedure as inExample 10 except that 5 wt % of Si was added to the positive activematerial.

Comparative Example 6

LiCoO₂ (manufactured by Nippon Chemical Co.) positive active materialpowder, polyvinylidene fluoride as a binder and Super P carbon as aconductive agent were added to N-methyl pyrrolidone as a solvent to makea positive active material slurry composition. At this time, the ratioof the positive active material powder: the binder: the conductive agentwas 94:3:3 wt %.

The positive active material slurry composition was coated Al-foil. Thecoated foil was dried in an oven at 120° C. for 3 hours and the driedfoil was pressed to produce a positive electrode. The positive electrodewas then assembled with a lithium metal foil (counter electrode).

The cycle life characteristics of the cells according to Example 8 andComparative Example 5 were measured. At this time, the charge anddischarge cycles were repeated one time to 0.1 C, three times to 0.2 C,10 times to 0.5 C and 51 times to 1 C, at 4.3 to 3.0V. The results areshown in FIG. 10. As shown in FIG. 10, the capacity of the cell usingthe active material of Example 8 was slightly reduced from about 140mAh/g to about 115 mAh/g after 51 cycles at high-rate (1 C charge anddischarge). Whereas, the capacity of the cell using the active materialof Comparative Example 5 was extremely reduced from about 140 mAh/g toabout 50 mAh/g after 51 cycles at a high-rate (1 C charge anddischarge). Accordingly, the active material of the present inventionhas more stability at a high temperature and a high rate (1 C charge anddischarge) than the conventional active material and has a limitedamount capacity reduction as well as good cycle life characteristics.

Differential scanning calorimetry (DSC) of the cells according toExample 8 and Comparative Example 5 after charging 4.3V were measuredand the results are presented in FIG. 11. As shown in FIG. 11, theexothermic peak area of the cell according to Example 8 with Si issmaller than that of Comparative Example 5 without Si. The exothermicpeak appeares due to the heat generated when the active material reactswith the electrolyte. As the exothermic peak area is small, thereactivity of the active material with the electrolyte is reduced, andthus it is stable. The oxygen decomposition temperature (218° C.) of thecell according to Example 8 is higher than that of Comparative Example 5(202° C.).

Accordingly, the cell of Example 8 has superior thermal stability. Thisis because after charging a lithium cell, a structure of the positiveactive material is converted from LiCoO₂ to Li_(1−x)CoO₂. As theLi_(1−x)CoO₂ active material is unstable, oxygen boned with metal (Co—O)decomposes according to increases in temperature. The decomposed oxygenmay react with electrolyte in a cell and cause the cell to explode.

The high-temperature cycle life characteristics and DSC results of thecells according to Examples 9-11 exhibited similar with Example 8 andthus, the cells are stable at a high-rate charge and discharge and havegood thermal stability.

EXAMPLE 12

A rechargeable lithium cell was manufactured by the same procedure as inExample 8 except that LiMi_(0.88)Co_(0.12)La_(0.01)O₂ positive activematerial powder was used.

Comparative Example 7

A rechargeable lithium cell was manufactured by the same procedure as inComparative Example 1 except that LiNi_(0.88)Co_(0.12)La_(0.01)O₂positive active material powder was used.

The cycle life characteristics of the cells according to Example 12 andComparative Example 7 were measured at room temperature (20° C.). Atthis time, the charge and discharge cycles were repeated three times to0.2 C, 10 times to 0.5 C, 66 times to 1 C, at 4.3 to 3.0V. The resultsare shown in FIG. 12. As shown in FIG. 12, the capacity of the cellusing the active material of Example 12 was slightly reduced at ahigh-rate (1 C charge and discharge) and room temperature (20□).Whereas, the capacity of the cell using the active material ofComparative Example 7 was extremely reduced at a high-rate (1 C chargeand discharge) and room temperature.

EXAMPLE 13

LiMn₂O₄ (manufactured by Nikki Co. under LM4) positive active materialpowder was mixed with Si powder. At this time, the amount of SiO₂ powderwas 1 wt % of the positive active material powder. The mixture,polyvinylidene fluoride as a binder and Super P carbon as a conductiveagent were added to N-methyl pyrrolidone as a solvent to make a positiveactive material slurry composition. The ratio of the positive activematerial and SiO₂ powder mixture: the binder: the conductive agent was94:3:3 wt %.

The positive active material slurry composition was coated on Al-foil.The coated foil was dried in an oven 120° C. for 3 hours and the driedfoil was pressed to produce a positive electrode. The positive electrodewas then assembled with a lithium metal foil (counter electrode), and alithium salt solution was added as an electrolyte to thereby fabricate acoin-cell type half-cell. The lithium salt solution included ethylenecarbonate and dimethyl carbonate (1:1 volume ratio) as a solvent and 1MLiPF₆ as a solute.

EXAMPLE 14

A rechargeable lithium cell was manufactured by the same procedure as inExample 13 except that 5 wt % of SiO₂ powder was added to the positiveactive material.

Comparative Example 8

LiMn₂O₄ (manufactured by Nikki Co. under LM4) positive active materialpowder, a polyvinylidene fluoride binder and a Super P conductive agentwere added to a N-methyl pyrrolidone solvent to make a positive activematerial slurry composition. At this time, the ratio of the positiveactive material powder: the binder: the conductive agent was 94:3:3 wt%.

The positive active material slurry composition was coated on Al-foil.The coated foil was dried in an oven 120° C. for 3 hours and the driedfoil was pressed to produce a positive electrode. The positive electrodewas then assembled with a lithium metal foil (counter electrode).

The cycle life characteristics at high temperature (50° C.) of theactive materials according to Example 13 and Comparative Example 8 weremeasured. At this time, the charge and discharge cycles were repeatedone time to 0.1 C, three times to 0.2 C, 10 times to 0.5 C and 86 timesto 1 C, at 4.3 to 3.0V. The results are presented in FIG. 13. As shownin FIG. 13, the capacity of the cell according to Example 13 wasslightly reduced after 86 cycles at a high-rate (1 C charge and 1 Cdischarge) and high temperature. Whereas, the capacity of the cellaccording to Comparative Example 8 was significantly reduced after 86cycles at a high-rate (1 C charge and 1 C discharge) and hightemperature. Accordingly, the active material of the present inventionhas more stability at high temperature and a high rate (1 C charge anddischarge) than the conventional active material and has a limitedamount capacity reduction as well as good cycle life characteristics.The high-temperature cycle life characteristics of cell according toExample 14 exhibited similar with that of Example 13 and thus, the cellaccording to Example 14 has more stability at high temperature and ahigh rate and also have a limited amount capacity reduction as well asgood cycle life characteristics.

EXAMPLE 15

A rechargeable lithium cell was manufactured by the same procedure as inExample 13 except that LiNi_(0.9)Co_(0.1)Sr_(0.002)O₂ (manufactured byHonjo Co.) was used as a positive active material.

EXAMPLE 16

A rechargeable lithium cell was manufactured by the same procedure as inExample 14 except that LiNi_(0.9)Co_(0.1)Sr_(0.002)O₂ (manufactured byHonjo Co.) was used as a positive active material.

Comparative example 9

A rechargeable lithium cell was manufactured by the same procedure as inComparative example 8 except that LiNi_(0.9)Co_(0.1)Sr_(0.002)O₂(manufactured by Honjo Co.) was used as a positive active material.

The cycle life characteristics of the cells according to Examples 15-16and Comparative example 9 were measured and exhibited similar resultswith FIG. 13. Accordingly, the positive active material according toExamples 15-16 has good high-temperature cycle life characteristics.

EXAMPLE 17

A rechargeable lithium cell was manufactured by the same procedure as inExample 13 except that LiCoO₂ (manufactured by Nippon Chemical Co. underC-10) was used.

EXAMPLE 18

A rechargeable lithium cell was manufactured by the same procedure as inExample 14 except that LiCoO₂ (manufactured by Nippon Chemical Co. underC-10) was used.

Comparative Example 10

A rechargeable lithium cell was manufactured by the same procedure as inComparative Example 8 except that LiCoO₂ (manufactured by NipponChemical Co. under C-10) was used.

The cycle life characteristics of the cells according to Examples 17-18and Comparative example 10 were measured and exhibited similar resultswith FIG. 13. Accordingly, the positive active material according toExamples 17-18 has good high-temperature cycle life characteristics.

EXAMPLE 19

A rechargeable lithium full cell was manufactured by a conventionalprocess and with a positive active material according to Example 13 anda mesophase carbon fiber (MCF) negative active material.

Comparative Example 11

A rechargeable lithium full cell was manufactured by the same procedureas in Example 19 except that the positive active material according toComparative Example 8 was used.

The cycle life characteristics at high temperature (60° C.) of the cellsaccording to Example 19 and Comparative Example 11 were measured and theresults are shown in FIG. 14. The cycle life characteristics resultswere obtained from a total of four cells (two Example 19 cells and twoComparative Example 11 cells). As shown in FIG. 14, a rechargeablelithium full cell according to Example 19 with SiO₂ has betterhigh-temperature cycle life characteristics than a cell without SiO₂.

EXAMPLE 20

LiCoO₂ (manufactured by Nippon Chemical Co. under C-10) positive activepowder was mixed with CaO (particle diameters of less than a 325 mesh).At this time, the amount of CaO was 0.1 wt % of the positive activepowder. The mixture, polyvinylidene fluoride as a binder and Super Pcarbon as a conductive agent were added to N-methyl pyrrolidone as asolvent to make a positive active material slurry composition. The ratioof the LiCoO₂ and CaO mixture: the binder: the conductive agent was94:3:3 wt %.

The positive active material slurry composition was coated on anAl-foil. The coated foil was dried in an oven at 120° C. for 3 hours andthe dried foil was then pressed to produce a positive electrode. Thepositive electrode was then assembled with a lithium metal foil (counterelectrode) and a lithium salt solution was added as an electrolyte tothereby fabricate a coin-cell type half-cell. The lithium salt solutionincluded ethylene carbonate and dimethyl carbonate (1:1 volume ratio) asa solvent and 1M LiPF₆ as a solute.

EXAMPLE 21

A rechargeable lithium half-cell was manufactured by the same procedurein Example 20 except that 0.5 wt % of CaO of the positive activematerial powder was added to the positive active material.

EXAMPLE 22

A rechargeable lithium half-cell was manufactured by the same procedurein Example 20 except that 1.0 wt % of CaO of the positive activematerial powder was added to the positive active material.

EXAMPLE 23

A rechargeable lithium half-cell was manufactured by the same procedurein Example 20 except that LiMn₂O₄ powder (manufactured by Nikki, Co.,under LM4) was used as a positive active material and 0.5 wt % of CaO ofthe positive active material was added to the positive active material.

EXAMPLE 24

A rechargeable lithium half-cell was manufactured by the same procedurein Example 20 except that LiNi_(0.9)Co_(0.1)Sr_(0.002)O₂ powder (Honjo,CO.) was used as a positive active material.

EXAMPLE 25

A rechargeable lithium half-cell was manufactured by the same procedurein Example 20 except that LiNi_(0.9)Co_(0.1)Sr_(0.002)O₂ powder (Honjo,Co.) was used as a positive active material and 0.5 wt % of CaO of thepositive active material was added to the positive active material.

Comparative example 12

A rechargeable lithium half-cell was manufactured by the same procedurein Example 20 except that CaO was not used.

Comparative example 13

A rechargeable lithium half-cell was manufactured by the same procedurein Example 22 except that CaO was not used.

Comparative example 14

A rechargeable lithium half-cell was manufactured by the same procedurein Example 24 except that CaO was not used.

After the cells according to Example 23 and Comparative Example 13 werecharged at 4.3V, differential scanning calorimetry (DSC) was measured inorder to identify the thermal stability of the positive active material.The results are presented in FIG. 15. It is shown from FIG. 15 thatendothermic peak and exothermic reactions occur in the electrodeaccording to Example 23. The endothermic peak occurs by the reaction ofCaO and the electrolyte in the electrode and the exothermic peak occursby the reaction of the remaining electrolyte and LiMn₂O₄. Whereas, theexothermic peak only occurs by the reaction of O₂ which generates fromthe charged electrode and the electrolyte.

The cycle life characteristics of the cell according to Example 23 weremeasured. At this time, the charge and discharge cycles were repeated100 times to 0.1 C, 0.2 C, 0.5 C and 1 C, between 4.3 and 3.0V at roomtemperature (20° C.) and high temperature (50° C.), respectively. Theresults are presented in FIG. 16. As shown in FIG. 16, the cellaccording to Example 23 exhibited good cycle life characteristics atroom temperature (20° C.) and high temperature (50° C.).

The high-temperature cycle life characteristics of the cells accordingto Examples 22 and 23, and Comparative example 13 were measured. At thistime, the charge and discharge cycles were repeated 100 times to 0.1 C,0.2 C, 0.5 C and 1 C, between 4.3 and 3.0V at 50 C. The results areshown in FIG. 17. As shown in FIG. 17, the cells according to Examples22 and 23 exhibited good cycle life characteristics than that accordingto Comparative example 13.

As described above, the rechargeable lithium battery using the positiveactive material composition of the present invention exhibits goodelectrochemical properties and thermal stability. The manganese-basedrechargeable lithium battery of the present invention exhibits improvedhigh temperature cycle life characteristics and the nickel- andcobalt-based rechargeable lithium battery exhibits good stability.

While the present invention has been described in detail with referenceto the preferred embodiments, those skilled in the art will appreciatethat various modifications and substitutions can be made thereto withoutdeparting from the spirit and scope of the present invention as setforth in the appended claims.

1. A rechargeable lithium battery comprising: a positive electrodeincluding a positive active material comprising a lithiated transitionmetal compound, and an additive, said additive at least one of Si, B,Ga, Ge, Ca, Mg, Sr and Ba; a negative electrode including a carbonaceousmaterial as an active material; and an electrolyte including an organicsolvent and a lithium salt dissolved in the organic solvent, whereinsaid positive active material composition is prepared by physicallymixing said positive active material, a binder in said organic solventin a form of slurry, wherein the additive is 0.01 to 10 wt % of thepositive active material, wherein the lithiated transition metalcompound is selected from the group consisting of compounds representedby formulas 1 to 13:Li_(x)MnA₂  (1)Li_(x)MnO_(2−z)A_(z)  (2)Li_(x)Mn_(1−y)M′_(y)A₂  (3)Li_(x)Mn₂A₄  (4)Li_(x)Mn₂O_(4−z)A_(z)  (5)Li_(x)Mn_(2−y)M′_(y)A₄  (6)Li_(x)BA₂  (7)Li_(x)BO_(2−z)A_(z)  (8)Li_(x)B_(1−y)M″_(y)A₂  (9)Li_(x)B_(1−y)M″_(y)O_(2−z)A_(z)  (10)Li_(x)NiCoA₂  (11)Li_(x)NiCoO_(2−z)A₂  (12)Li_(x)Ni_(1−y−z)Co_(y)M″_(z)A₂  (13)  wherein 1.0≦x≦1.1, 0.01≦y≦0.1,0.01≦z≦0.5, M′ is at least one transition metal or lanthanide metalselected from the group consisting of Al, Cr, Co, Mg, La, Ce, Sr and V,M″ is at least one transition metal or lanthanide metal selected fromthe group consisting of Al, Cr, Mn, Fe, Mg, La, Ce, Sr and V, A isselected from 0, F, S or P, and B is Ni or Co.
 2. The rechargeablelithium battery of claim 1, wherein said organic solvent isN-methylpyrrolidone.
 3. The rechargeable lithium battery of claim 1wherein the lithiated transition metal compound is a compoundrepresented by formula:Li_(x)BA₂ where 1.0≦x≦1.1, A is selected from O, F, S or P, and B is Nior Co.
 4. The rechargeable lithium battery of claim 1 wherein thelithiated transition metal compound is a compound represented byformula:Li_(x)BO_(2−z)A_(z) where 1.0≦x≦1.1, 0.01≦z≦0.5, A is selected from O,F, S or P, and B is Ni or Co.
 5. The rechargeable lithium battery ofclaim 1 wherein the lithiated transition metal compound is a compoundrepresented by formula:Li_(x)B_(1−y)M″_(y)A₂ where 1.0≦x≦1.1, 0.01≦y≦0.1, M″ is at least onetransition metal or lanthanide metal selected from the group consistingof Al, Cr, Mn, Fe, Mg, La, Ce, Sr and V, and A is selected from O, F, Sor P, and B is Ni or Co.
 6. The rechargeable lithium battery of claim 1wherein the lithiated transition metal compound is a compoundrepresented by formula:Li_(x)B_(1−y)M″_(y)O_(2−z)A_(z) where 1.0≦x≦1.1, 0.01≦y≦0.1, 0.01≦z≦0.5,M″ is at least one transition metal or lanthanide metal selected fromthe group consisting of Al, Cr, Mn, Fe, Mg, La, Ce, Sr and V, A isselected from O, F, S or P, and B is Ni or Co.
 7. The rechargeablelithium battery of claim 1 wherein the lithiated transition metalcompound is a compound represented by formula:Li_(x)NiCo₂ where 1.0≦x≦1.1, and A is selected from O, F, S or P.
 8. Therechargeable lithium battery of claim 1 wherein the lithiated transitionmetal compound is a compound represented by formula:Li_(x)NiCoO_(2−z)A_(z) where 1.0≦x≦1.1, 0.01≦z≦0.5, and A is selectedfrom O, F, S or P.
 9. The rechargeable lithium battery of claim 1wherein the lithiated transition metal compound is a compoundrepresented by formula:Li_(x)Ni_(1−y−z)Co_(y)M″_(z)A₂ where 1.0≦x≦1.1, 0.01≦y≦0.1, 0.01≦z≦0.5,M″ is at least one transition metal or lanthanide metal selected fromthe group consisting of Al, Cr, Mn, Fe, Mg, La, Ce, Sr and V, and A isselected from O, F, S or P.